The invention relates to an apparatus for producing collapsible containers with a deformable tubular body formed of a thermoplastic foil strip and a closing cap. The apparatus includes a continuously moving feed device for a laminated strip, a two-stage shaping device with a shaping tube and a mandrel and continuously driven transport belts, a welding unit, cooling device which may include means for supplying air into the shaping device for reducing friction, a cutting device, a continuously operating transporting device, and spindles which are arranged on a turntable and can be supplied to processing stations, for connecting the foil tubes produced with the closing caps.
Apparatus for forming tubes are described in U.S. Pat. Nos. 3,388,017 and 3,778,321. U.S. Pat. No. 3,388,017 describes an apparatus for producing tubular bodies of a thermoplastic strip material wherein the strip material is carried on a driven conveying belt having a smaller breadth than the strip material. The strip material is introduced jointly with the belt into a split shaping tube which is open at the top. Furthermore, two driven belts are provided of which one is guided in grooves in the mandrel and the other is so arranged that the overlapping parts of the tube strip are guided during passage through the shaping body so as to be clamped by the action of pressure by means of the two belts. Heat transfer when welding the seam is ensured by contact heating which is brought about by virtue of heating acting through the transport belt onto the foil.
This apparatus has the following disadvantages: The strip to be welded is introduced into the shaping body by a conveying belt, and this belt makes the apparatus as a whole more complicated and in this respect it is necessary to ensure that the conveying belt is always so guided that it does not in any case come into the lap zone of the tube strip, since this causes misfunction and impairment of the quality of the tube strip produced. In the case of a known apparatus this is achieved by preshaping the strip with a guide roller on the one hand and by the further feature that the passage opening of the shaping block has two different diameters, that is to say on the one hand only for the passage of the tube strip and on the other hand for the passage of the tube strip and the conveying belt and therefore in the abutting zone lateral recesses have to be provided in the cross-section which give the conveyer belt some lateral play. Furthermore, for this purpose, guide rollers have to be provided at the bottom.
Furthermore, as a heat transfer element, the conveyor belt is subjected to extreme thermal loading since the same belt is passed through the welding zone and also through the cooling zone. This leads to the further disadvantage that both the transfer of heat and also the removal of it can only be indirect, that is to say through the conveyor belt.
All these features render the apparatus extremely complicated and owing to the necessary recesses and spaces allowing for play of the belts, it is not possible to produce any exactly round cross-section of the tube body even at positions remote from the joint seam and accordingly the shape of the tube body and therefore its final appearance are impaired. Furthermore, the conveyor belt is continuously deformed in various directions by the guide rollers and the shaping to produce half a tube and it is caused to slide on the shaping block so that it is subject to rapid wear and must often be replaced, something which leads to substantial losses in production time.
Furthermore, heating by contact offers a relatively low efficiency and this in turn results in limitations in the speed of operation. The action of heating by contact depends upon the engagement area, that is to say on the foil and it is difficult to check and leads to substantial tolerances.
Since each of the three conveyer belts must be driven separately and, in the case of the necessarily elastic construction of the belts absolutely synchronous drive is not possible, additional difficulties occur, which reduce the quality of the tube bodies produced. The result of all these difficulties taken together is that such forms of apparatus have not become accepted in the tube making machine market.
U.S. Pat. No. 3,778,321 describes an apparatus for producing collapsible containers having a turntable with several rotary spindles, which can be supplied to different processing stations. A foil strip is wound up on to a spindle with overlap, cut off and longitudinally welded or, respectively, bonded and one end is so folded that a closure cap can be mounted on it, which is fixed in position by welding or bonding.
In the case of this apparatus, substantial difficulties arise as regards ensuring a straight cut edge, even overlap and production of blanks with a constant diameter and with a weld seam of constant shape. Furthermore, the production of the head part by folding, donning and joining a closure cap is very elaborate and ultimately leads to a poor appearance of the joint, more particularly if the latter is welded, so that this apparatus has never come into use for industrial tube production. Furthermore, with this apparatus it is not possible to produce on a large scale since the rolling up, cutting off and welding oerations have to be carried out one after the other in definite stages on one spindle.
In accordance with a further proposal, closure heads were to be produced on the tube bodies by injection molding, something which leads to the well-known disadvantages which can occur in the case of periodic injection molding and furthermore this leads to low output speeds of the apparatus as a whole.